While the principles and features of the present invention are applicable to the screening of a wide variety of materials, they are of particular utility in the screening of food products, e.g., meat, such as de-boned poultry pieces, and will be discussed and explained in that context.
Screening de-boned poultry pieces for the presence of bone and cartilage fragments or other defects is of vital concern to the poultry industry. Such fragments left in the meat can result in product liability actions and shipment returns for rework, with staggering cost implications. Manual "feeling" techniques are not accurate, pose a risk of spreading microbial contamination, are labor intensive, and are generally incapable of locating small fragments in the meat. As a consequence, systems have begun to be used in bone and cartilage screening which use typical X-ray transmission radioscopy techniques such as are used in airport security scanning. In such a system, differences in density between the meat and foreign matter are registered on the viewing screen. However, the density difference between the meat and bone or cartilage fragments is small, and material density variations in the meat created by water or fat, as well as meat thickness variations make it difficult for simple transmission X-ray techniques to discriminate accurately. As a consequence, with the X-ray transmission screening, false positive readings as high as fifty percent (50%) are not uncommon in poultry screening. Obviously, such lack of reliability can lead to increased expense in the processing of de-boned chicken parts, and can cause the rejection of parts that are, in actuality, perfectly acceptable.
In addition to transmission X-ray techniques, there are, in the prior art, systems which utilize "backscatter" detection of radiation from Compton scattering to enhance the image produced by the transmission radiation. A variation of such a system is shown in Friddell U.S. Pat. No. 4,974,247, wherein Compton radiation (backscatter) is detected along with reflected or backscattered transmission radiation from a reflector or illuminator to produce an enhanced radiographic image. While such an arrangement is not proposed specifically for poultry processing, it would appear that the basic principles thereof could be adapted to poultry screening.
In U.S. Pat. No. 3,944,822 of Dzubay there is shown an X-ray system for analyzing samples, such as, for example, a pellet of compressed orchard leaves, which relies upon photon fluorescence emitted by the sample when it is bombarded with X-rays. Different materials present in the sample have different characteristic florescence, hence, an analysis of the sample reveals the basic elements contained therein. The invention is directed to reducing the amount of Compton scattering relative to the florescent peaks, thereby enhancing the sensitivity of the fluorescent analysis. However, there are severe limitations to the detection of fluorescence, and hence, element composition, from small objects such as bone and cartilage pieces embedded within the bulk of a piece of chicken, for example. These limitations result from the fact that such materials, i.e., bone and cartilage fragments, have relatively low density, resulting in fluorescent intensities that are weak. In addition, there is substantial absorption of the fluorescence of, for example, calcium in bones and potassium in cartilage by the surrounding muscle and fat tissue of the sample. As a consequence, fluorescence analysis such as shown in the Dzubay patent is not practical for the rapid, continuous screening of chicken pieces in a processing production line. In such a production milieu, fluorescence is only useful for identifying foreign matter, such as oil or metal filings, on the surface of the sample, and thus is not practical for identifying bone and cartilage fragments.
various other prior art arrangements utilizing back scattering and/or fluorescence for sample screening are shown in Badono U.S. Pat. No. 4,817,122, et al., Page U.S. Pat. No. 4,486,894 et al., Pavlik U.S. Pat. No. 3,710,104, and Goldman U.S. Pat. No. 3,375,369 et al. None of these arrangements appears to lend itself to use in screening poultry products, for example, for the reasons set forth hereinbefore.
In the screening of poultry pieces, for example, it is desirable to locate and identify fragments of bone and cartilage with a high degree of accuracy and at a high rate of speed. Thus far, the prior art systems of screening samples fail in achieving one or more of these desiderata, with the consequence that the problems of product liability and shipment returns remain substantially the same as heretofore.